Electronic dryer

ABSTRACT

A dryer includes a cabinet having a drying chamber mounted therein. A blower connected by a duct to the drying chamber draws air through the chamber from openings provided in both the chamber and the cabinet. The output of a source of microwave energy is introduced into the duct which functions as a waveguide to direct the microwave energy to the drying chamber. As the microwave energy heats and causes to vaporize the water in the articles to be dried, the evaporated moisture is drawn out of the chamber by the air flowing therethrough and is exhausted to atmosphere. In one embodiment, the dryer is formed as a clothes dryier wherein the drying chamber takes the form of a rotating tumbling drum mounted within the cabinet and the air entering the drum is preheated.

United States Patent 1191 Staats 14 1 Dec. 17, 1974 1 ELECTRONIC DRYER3,605,272 9/1971 Boucher 1. 34/1 1 t EJSt t L 'll,K. [75] men or Jamesaa 5? Oulsvl e y Primary Examiner-Charles J. Myhre [73] Assignee:General Electric Company, Assistant Examiner-Paul Devinsky Louisville,Ky- Attorney, Agent, or Firm-Frederick P. Weidner; 122 Filed: June is,1973. Franc [21] Appl. No.: 370,863 [57] ABSTRACT A dryer includes acabinet having a drying chamber U.S.. Cl 34/1, 3 219/1055 mountedtherein. A blower connected by a duct to the [51] Int. Cl. F26!) 3/34drying chamber draws air through the chamber from Field Of Searchopenings provided in both the chamber and the cabi- 219/1055 net. Theoutput of a source of microwaveenergy is introduced into the duct whichfunctions as a waveguide [56] Refere ces Cite to direct the microwaveenergy to the drying chamber. UNITED STATES PATENTS As the microwaveenergy heats and causes to vaporize 2,511.8 6/1950 Frye I I I I I I I Iv U 34 the water in the articles to be dried, the evaporated 31926427/l965 Hughes 34/55 moisture is drawn out of the chamber by the an flow-3,276,138 /1966 m2 34/1 ineths sthr sn nd .isszslzausttsl..teatmssphstqi3,410,116 11/1968 Levinson.... 68/4 one embodiment, the dryer is formedas a clothes 3,440,383 4/1969 Smith 219/1055 dryier wherein the dryingchamber takes the form of a 3,440,335 4/1969 Smith 219/10-55 rotatingtumbling drum mounted within the cabinet 3,446,929 5/1969 219/1055 andthe air entering the drum is preheated. 3,458,755 7/1969 Staats 315/3951I 3,546,783 12/1970 Candor et a1. 34/1 9 Claims, 5 Drawing Figures I aM2 /Z6'2/ I 5 A52 H l 28 e2 U0 an? L 6'6 1 ELECTRONIC DRYER BACKGROUNDOF THE INVENTION This invention relates generally to drying machines.More specifically, it relates to machines for drying wet materialutilizing microwave radiation as a source of energy for causingevaporation, and a preheated air flow for removing the evaporatedmoisture.

The use of ultrahigh frequency electromagnetic energy,'.such asmicrowave energy, for heating is, of course, well known in the art.Devices producing microwave energy have found utility in industrialheating processes for some years and more recently have been utilizedfor cooking on commercial and home usage bases. 'The industrial uses ofmicrowave energy have included the utilization of microwave devices fordrying such things as painted articles or articles which have been gluedor caused to adhere to each other by the use of some kind of adhesive.Typically, in drying applications the microwave energy has been suppliedby providing a radiator in the form of a coil which is excited by amicrowave source and radiates energy to wet articles caused to passwithin the turns of the coil. Such applications have, of necessity,involved some means for feeding the article to the area encompassed bythe coil, such means usually including some kind of conveyor or articletransport device.

There are, however, numerous situations where it is desired to dryobjects, yet, it is uneconomical or impracticable to utilize conveyorsfor transporting the articles to and from an area encompassed by amicrowave coil radiator. Consequently, the drying of articles in achamber becomes desirable. In order to permit drying to. proceed rapidlyand efficiently when a chamber is used, it is desirable to provide meansfor removing from the chamber the moisture evaporated from the articles.

There are, of course, other applications of microwave energy for heatingarticles in a chamber, as for instance, cooking. The article to beheated is placed within the chamber, an oven, and the energy is coupledto the interior of the chamber. In this kind of application, of course,drying of the food is the last thing that is desired for the removal ofwater from cooked foods generally adversely affects their taste andtexture.

Therefore, it is an object of this invention to provide a novel dryingmachine wherein microwave energy is utilized within a chamber toevaporate moisture from wet materials therein, and a preheated airstream is utilized to remove the evaporated moisture from the chamber.

It is a further object of this invention to provide a novel dryingmachine which utilizes heated moving air to remove moisture evaporatedfrom wet objects by the microwave energy and which utilizes a singleconduit functioning as part of the microwave energy transmitting meansand as part of the air moving means so as to provide a relativelyeconomical and compact arrangement which at the same time is efficientin its operation.

A particular application wherein drying apparatus in accordance with theinvention may find utility is a clothes drying machine such as is usedin the home or commercial operations. Such machines have rotatingclothes tumbling drums mounted within a protective cabinet. Included inthe space between the tumbling drum and the protective cabinet are themeans for mounting the drum for rotation, a motor for rotating the drumand a blower to blow dry, heated air over and through the clothesas'they are tumbled within the drum. A door is provided to give accessthrough the cabinet to the drum interior to permit the user to place wetclothes within the drum and to remove the dry clothes therefrom. It isbelieved that a considerable advantage in performance and the economicsof manufacture can be achieved by the utilization of apparatus inaccordance with this invention in such a dryer, and particularly wherethe clothes tumbling 'drum and the conduit or duct for directing airflowthrough the drum are advantageously formed in the customary manner fromsheet metal.

It is another object of this invention to provide a clothes dryer whichutilizes microwave energy as a drying medium and which does not requirea substantial reconstruction of a conventional clothes dryer.

It is still another object of this invention to provide a clothes dryerutilizing microwave energy as a drying medium which is safe for use byrelatively unskilled op erators as simple but effective means isprovided to prevent microwave radiation from entering the atmosphere orany place where a user could inadvertently place his hands or any otherpart of his body.

It is a still further object of this invention to provide a means forautomatically interrupting the transmission of microwave energy to adrying chamber when all of the wet material therein has been dried to apredetermined degree of dryness.

It is still another object of this invention to provide a dryerutilizing microwave energy wherein automatic control of the sourceofmicrowave energy is effected without the necessity of any sensing ortiming devices so as to interrupt the transmission of microwave energyto the drying chamber when all of the wet material has been dried to apredetermined degree of dryness.

SUMMARY OF THE INVENTION In accordance with the present invention thereis provided an electronic dryer comprising a casing within which ismounted a drying chamber for accommodating items to be dried. Alsoincluded is air circulating means and a conduit associated with thedrying chamber for circulating a stream of air therethrough andgenerating means is provided which is adapted to produce ultrahighfrequency electromagnetic energy at a predetermined frequency. Means areprovided for coupling the generating means with the conduit fortransmitting energy from the generating means to the conduit, theconduit serving both as an air duct and as a waveguide for theelectro-magnetic energy. The moisture evaporated from wet articlesplaced in the drying chamber is carried from the drying chamber by theair stream and is exhausted through the conduit to the exterior of thecabinet.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofapparatus embodying the invention;

FIG. 2 is a side elevational view partially broken away and partially insection illustrating a preferred embodiment of the invention in aclothes drying machine;

FIG. 3 is a partial side elevational view of the clothes drying machineshown in FIG. 2, partially broken away and partially in section,illustrating the blower apparatus and drive machinery;

FIG. 4 is a front elevational view in partial section taken generallyalong the lines 44 in FIG. 2 illustrating the flow path for air andmicrowave energy; and

FIG. 5 is a schematic diagram of a control circuit embodying an aspectof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, thereis shown an electronic dryer in accordance with the present invention.The apparatus includes an outer casing or cabinet 42 preferably of sheetmetal construction. The cabinet 42 is provided with air inlet means 12and air egress means such as exhaust 140 whereby air may enter thecabinet enclosure from the atmosphere, flow through the interior thereofand be thereafter exhausted to the atmosphere. Air inlet 12 is coveredby a screen 80 which prevents the undesirable entrance of largeparticles of foreign matter into the enclosure. Air is drawn into andexhausted from the cabinet 42 by air circulation means such as a blower128 mounted therein and driven by a motor 74. Mounted within the cabinet42 is a microwave impermeable drying chamber 56 into which is placed theitem or items to be dried. Drying chamber 56 is provided with an airingress 82 and air outlet means, such as a plurality of perforations126, in a spaced-apart relationship, whereby air flowing through chamber56 will readily remove moisture evaporated from the articles being driedtherein. As can be readily seen, air ingress 82 and outlet means 126 aredepicted in FIG. 1 as perforations in opposing sides of the dryingchamber 56. A conduit 130 connects the air outlet means or perforations126 through the input of the blower 128. By virtue of the arrangementillustrated, when the blower 128 is operating, air is drawn into cabinet42 through air inlet 12 and flows along the path indicated' by the airshown in solid lines, into the drying chamber 56 through the air ingress82 and out through the perforations 126 to the conduit 130, to blower128 which vents to atmosphere.

In accordance with one embodiment of this invention, a heat source 88may be positioned within the cabinet 42 so as to be in the path of theair flow into the drying chamber 56 through air ingress 82. The heatsource is shown as being of the electrical resistance type; however, inanother embodiment of this invention, heat source 80 may be a gasburner, the flame of which heats the air flowing into drying chamber 56.

Mounted within the cabinet 42 adjacent the air inlet 12 is generatingmeans 150 for producing ultrahigh frequency electromagnetic energy suchas microwave energy. Generating means 150 may be any of several wellknown types, but is preferably a cross-field discharge device, or amagnetron of the type disclosed in U.S. Pat. No. 3,458,755-Staats,issued July 29, 1969 and assigned to the same assignee as the presentinvention. Coupled to the output terminals of the generating means 150is a coaxial transmission line 152, transmission line 152 terminating ina section of conduit 130. The termination of line 152 is provided byantenna means such as antenna 158 coupled to the inner conductor of thecoaxial line 152.

Antenna 158 is adapted to radiate microwave energy into conduit 130which serves as a waveguide for propugating the microwave energy towarddrying chamber 56. Disposed in the center of the air outlet means 126 isa microwave window 162 which is closed by a sheet or cover of microwavetransparent material. More particularly, the microwave energy radiatedby antenna 158 into conduit is propagated upwardly therealong, as shownby the dashed arrows, entering the dry ing chamber 56 through microwavewindow 162. Window 162 has a perimeter which is greater than onewavelength of the frequency of operation of the magnetron such that itmay function for its intended purpose as is well known to those skilledin the art.

To prevent transmission of the microwave energy through the conduit 130toward the blower 128, a microwave reflector such as wire mesh screen138 is provided. Wire mesh screen 138 serves to reflect the microwaveenergy and confine it to the conduit 130 while at the same timepermitting passage of air drawn through conduit 130 by blower 128.Likewise, the perforations forming air ingress 82 will not permit thepassage of microwave energy therethrough, such that the microwave energyis confined within the microwave impermeable drying chamber 56.

In operation, the items to be dried are inserted into the drying chamber56 by suitable means (not shown in this FIGURE but shown and describedlater in connection with a clothes dryer embodying the invention) andthe motor 74 is energized to cause the blower 128 to operate. Theoperation of the blower 128 drawing air through the air outletperforations 126 and conduit 130 creates an area of reduced pressure indrying chamber 56 and thereby generates a stream of air through thedrying apparatus. This stream of air is drawn into the cabinet andthrough the air inlet 12. As shown by the solid line arrows, the airflow sweeps over the generating means or magnetron 150 to cool themagnetron and heat the air to a small extent, being then drawn upwardlythrough the air ingress 82 into the drying chamber 56. Prior to enteringthe drying chamber, the air is further heated by heat source 88 to apredetermined temperature range, the upper limit of which is less thanthat temperature which would cause damage to the items being dried, suchas by physical deterioration or scorching or burning. The elevatedtemperature of the air flowing through the drying chamber 56 is ofcourse desirable, as the moisture carrying capacity of the air isincreased with elevated temperature. Upon entering the drying chamber56, the air is swept over the articles to be dried, picking up moisturetherefrom, then flowing out of the drying chamber 56 through air outlet126 to be exhausted to atmosphere by a conduit 130 and blower 128.

At or about the same time that the blower motor 74 is energized,magnetron 150 is energized to begin producing microwave energy at theoutput terminals thereof at a predetermined ultrahigh frequency,preferably in this embodiment at 915 MHz. This microwave energy istransmitted along the transmission line 152 and is radiated by theantenna 158 into conduit 130. Conduit 130 is dimensioned to act as awaveguide at the frequency of operation of the generating means 150 andpropagates the microwave energy toward microwave window 162. Aspreviously pointed out, mesh screen 138 serves to reflect the microwaveenergy impinging thereupon to confine it such that it may not reachblower 128, while at the same time permitting air to be drawn throughconduit 130 toward blower 18. Microwave energy is transmitted fromconduit 28 through microwave window 162 into the interior of dryingchamber 56.

In the drying chamber, the microwave energy is selectively absorbed bythe wettest portions of the items to be dried, serving to heat andvaporize the moisture or water content of the items in a manner wellknown in the art. As the water content of the wet items is vaporized bythe microwave energy, it is freed from the items and is carried from thedrying chamber 56 by the air stream passing therethrough as describedabove. In this manner, the wet articles are quickly and efficientlydried to any desired degree of dryness. It is a quality of microwavedrying that the wettest articles absorb the most microwave energywhereby the drying of such articles is speeded considerably while at thesame time articles which are not quite so wet are prevented from beingscorched. Thus, there is achieved a rapid and uniform drying of a loadof items of varying degree of wetness.

It will also be noted that the heating and vaporizing of the moisture inthe articles to be dried is facilitated by'the fact that the stream ofair can be heated before it passes through the drying chamber 56 toeffect conventional convection drying of the wet articles. As previouslyset forth, this heating of the air stream is accomplished by its passageover heat source 88. Some additional preliminary heating of the airstream is effected by the passage of the air stream over generatingmeans 1 50'as the air stream enters the cabinet 42 through the air inlet12. Thus while the air stream serves to cool the generating means 150,the heat drawn therefrom is utilized to provide additional warming ofthe air stream to enhance its drying affect on the wet articles in thedrying chamber 56. Similarly, the air flow may serve to 'cool the powersupply (not shown in FIG. 1) for the generating means, by positioningthe power supply in the air flow path in the same manner as thegenerator or generating means 150.

As previously stated, a particular embodiment of this invention, whereinits objects and advantages are readily employed, is a domestic clothesdryer. FIG. 2 illustrates such a clothes dryer generally designated byreference numeral 41. A dryer, in accordance with this invention, mayutilize a mechanical structure which is similar to that disclosed in US.Pat. No. 3,009,259 Simpson, assigned to the same assignee as the presentinvention, the disclosure of which is incorporated herein by reference.

The dryer includes an outer casing or cabinet 42 comprising a top wall44, a bottom wall 46, a pair of opposite side walls 48, a front wall 50and a rear wall 52, all preferably of sheet metal construction. Mountedat the rear end of top wall 44 is a panel 54 on which are mounted thecontrols of the dryer. A drum 56 having a generally cylindrical sidewall 58, a generally circular rear end wall 60 and an annular front wall62, is preferably of sheet metal construction and is mounted within thecabinet 42 for rotation about a substantially horizontal axis. Thecylindrical side wall 58 of drum 56 is provided on the inner surfacethereof with a plurality of tumbling ribs 64 for engaging the fabric orclothing as the drum rotates to cause tumbling of the clothing in a wellknown manner. The drum 56'thus defines a microwave impermeable dryingchamber for accommodating wet clothing to be dried.

In order to support and rotate the drum 56, recessed cylindrical wall 66and 68 are disposed at the rear and front ends respectively of thecylindrical side wall 58. The front recessed portion 68 of the drum sidewall 58 is rotatably supported within the cabinet 42 by means of a pairof idler roller wheels 70, one of which is shown in FIG. 3.

As also seen in FIG. 3, the rear recessed wall portion 66 of thecylindrical side wall 58 is supported by a drive roller wheel 72 drivenby an electric motor 74 which also drives the blower as will besubsequently described. The idler roller wheels and the drive rollerwheel 72 constitute elements of a known home dryer as shown in thepatent to Simpson, mentioned above. Referring again to FIG. 2, the axisof rotation of the drum 56 is maintained in vertical alignment of thedrive roller wheel 72 by the inner action of a stub shaft 76 secured atthe center of circular rear end wall 60 and an elongated slot 78 formedin a member to be hereinafter described which is supported from the rearwall 52 of the cabinet 42. The slot 78 has a relatively large verticaldimension and a relatively small horizontal dimension only slightlygreater than the diameter of the shaft 76, whereby the slot 78 preventssidewise motion of the shaft 76 therein but accommodates a small degreeof vertical motion of the shaft 76 and the drum 56 resulting from thedriving motion imparted thereto by the driving roller wheel 72. Thedetails of construction of the shaft 76 and its cooperation with theslot 78 are disclosed in the aforementioned US. Pat. No. 3,009,259.

Having described the dryer drum 56 and the means for supporting it forrotation in the cabinet 42, the means for providing an air flow throughthe cabinet and drum will now be described. Air enters the cabinet 42through an air inlet formed by air inlet screen 80 disposed at thebottom of rear wall 52, and thereafter enters the drying drum 56 throughair ingress means formed as an annular array of perforations 82 in therear end wall 60 of drum 56.

Rigidly secured to the rear wall 52 of cabinet 42 by suitable means,such as welding at points 84, is an outer baffle member 86 havingsecured on the inner surface thereof a plurality of heating elements 88comprising a heat source. The heating elements 88 may be of theelectrical resistance type and may be generally annular in shape so asto be substantially coextensive with the annular array of perforations82 in the rear wall 60 of the drum 56. An inner baffle member 90 isrigidly secured about the periphery thereof to the rear wall 60 of thedrum 56 and is disposed within the outer baffle member 86. The innerbaffle member 90 is slightly smaller than the outer baffle member 86 andis disposed a slight distance inwardly therefrom and cooperatestherewith to form an annular air inlet passage 92 therebetween. Theinner baffle member 90 is further provided with an annular series ofopenings 94 opening into the rear wall 60 of drum 56. Thus, a path forair flow is provided through the air inlet passage 92 between the bafflemembers over the heating elements 88 through the openings 94 andperforations 82 into the drum 56. It will be noted that the inner bafflemember 90 has a depressed central portion 96 to which is secured abracket 98 supporting shaft 76 set forth above.

Access means for placing articles to be dried in the drum 56 and forremoval therefrom are provided by a substantially circular accessaperture or opening 100 formed in front wall 62 of drum 56 and by ahollow microwave impermeable door 102 preferably of sheet metalconstruction provided in front wall 50 of cabinet 42 in alignment withthe access opening 100. The upper portion of the front wall 50 of thecabinet 42 is provided with a doorway defined therein by a door frame orelectrically conductive door seat 104 which comprises a part-cylindricalwall sloping inwardly from the drum 56 and having a substantially flathorizontal bottom portion 106, which effectively truncates the upperportion of the part-cylindrical door seat 104 and slopes inwardly towardthe drum. The door seat 104 is disposed substantially in axial alignmentto the access opening 100 of drum 56 with its cylindrical portion beingsubstantially concentric with access opening 100 and the inner edge ofthe door seat 104 being received within a cylindrical flange 108integrally formed with front wall 62 and spaced radially inward a slightdis tance therefrom to provide clearance to permit free rotation of thedrum 56.

Mounted on the outer surface of the door seat 104 around the peripherythereof is a flange 110 having secured thereto a ring seal 112preferably formed of feltlike material and extending rearwardlytherefrom and engaging the front wall 62 of the drum 56 in a sealingrelationship so as-to prevent leakage of air from the drum 56 betweenthe flange 110 and the door seat 104. The door 102 is hingedly mountedon the front wall 50 of the cabinet 42 and includes an outer imperforatesection 114 generally rectangular in shape, and a ho]- low inwardlyextending portion 116 which is shaped complementary to the door seat 104and is closed at its inner end by the inner wall 118. The door 102 ismovable between an open position extending outwardly from the front wall50 substantially normal thereto and a closedfposition wherein the hollowinwardly extending portion 116 is received within the door seat 104 andcloses the access opening 100. The inwardly extending portion 116 of thedoor 102 has a flat bottom portion 120 provided with a generallyrectangular opening 122 therein spaced complementary to an opening 124in the flat horizontal bottom portion 106 of door seat 104 and disposedin registry therewith when the door is in its closed position. The innerwall 118 of the door 102 is provided with a plurality of microwaveimpermeable perforations or openings 126 therethrough communicating withthe hollow interior of the door 102 whereby air may flow from the drum56 through openings 126 and the hollow interior of door 102 to openings122 and 124.

Referring now to FIGS. 2, 3 and 4, the means by which air flows from thedrum 56 through perforations 126 and inner wall 118 of the door 102 tobe exhausted from the cabinet 42 will be described. The intake of acentrifugal blower 128 driven by electric motor 74 is connected to aconduit such as duct 130 which includes a front section 132 and a rearsection 134. The front section 132 is substantially rectangular incrosssection and extends upwardly along the front wall 50 of the cabinet42 from the lower end thereof and then terminates in an open upper endconnected to the flat bottom section 106 of the door seat 104 inregistry with the opening 124 therein. The rearward extending portion136 of the front section 132 is connected to the rear section 134 asbest shown in FIG. 3. Spanning the joint between the front and rearsections of the duct 130 is a wire mesh screen 138 which serves as areflector of microwave energy as will be hereinafter described. Theexhaust of centrifugal blower 128 is directed to an outlet or exhaustopening 140.

Carried by the flat bottom portion 106 of door seat 104 in the opening124 therein is a lint trap generally designated by the numerals 141 andwhich is provided with a mounting collar 142 and a filter screen 143.The mounting collar 142 is substantially rectangular in shape and isprovided with a screen supporting flange 144 shaped complementary to theopening 124 and extending downwardly into the open upper end of thefront duct section 132. Integral with the upper end of the screensupporting flange 144 and extending outwardly therefrom is a mountingflange 146 which overlies the bottom of the door seat 104 about theperiphery of the opening 124 therein for supporting the lint trap 141thereon.

The screen 143 is preferably formed of a fine wire mesh and defines abag or basket having an open upper end embedded in a screen supportingflange 148 on the mounting collar 142 and having a closed lower endextending downwardly into the upper end of the front duct section 132.The screen is shaped complementary to the front duct section and isspaced a slight distance inwardly therefrom so as to provide a clearancebetween the screen and the inner surface of the front duct sectionaround the entire periphery thereof. In particular, the upper end of thescreen is embedded in the mounting collar 142 a slight distance inwardlyof the inner surface of the duct section 132 so as to be spacedtherefrom by the thickness of the screen supporting flange 148, theperimeter of which is dimensioned so as to be greater than thewavelength of the frequency of operation of the microwave generatorprovided. The mounting collar 142 is preferably formed of plastic orother microwave transparent material as will be explained more fullyhereinafter, Disposed in the bottom of the cabinet 42 adjacent the airinlet screen 80 is a magnetron 150 for producing microwave energy of apredetermined high frequency, and may be of the type disclosed in US.Pat. No. 3,458,755, as mentioned above.

Coupled to the output terminals of the magnetron 150 is a coaxialtransmission line 152 which includes a hollow outer conductor 154 andinsulated therefrom by suitable means, an inner conductor 156. Thetransmission line 152 terminates at the front section 132 of the duct130, the outer conductor 154 being connected to the duct section 132 andthe inner conductor 156 terminating in antenna means such as an antenna158. The antenna 158 extends into the duct section and both the innerconductor 156 and the antenna 158 are insulated from the duct sectionand the outer structure by an insulating spacer 160. The antenna 158 isadapted to radiate microwave energy into the front section 132, thisfront section serving as a waveguide for propagating microwave energytoward the drum 56 as will be described in detail below.

There is provided in the inner wall 118 of the door 102 a microwavewindow generally designated by the numeral 162 and including a generallycross-shaped opening 164 covered by a plastic sheet or cover 166 whichis formed of suitable microwave transparent material. The perimeter ofthe opening 164 is greater than one wavelength of the frequency ofoperation of the magnetron 150 whereby the opening serves as a microwaveaperture or window as is well known to those skilled in the art.

microwave energy but the mountingcollar 142 is formed of a materialwhich is transparent to that energy and as the perimeter of the screensupporting flange 144 is greater than the wavelength of the frequency ofoperation of the generating means, the flange 148 thereof serves as amicrowave aperture for the microwave energy. The microwave energy thenpasses through the opening 124 in the door seat 104 which also has aperimeter greater than one wavelength of the frequency of operation ofthe generator, and thence into the hollow interior of the door 102. Fromthe door 102 the microwave energy passes through the microwave window162 into the drying chamber of the drum 56. It will be noted that thewindow 162 is necessary to permit the transmission of microwave energythrough the inner wall 118 of the door since the perforations 126therein are too small to permit the transmission of such energytherethrough. Similarly, the perforations 82 in the rear wall 60 of thedrum 56 will not permit the passage of microwave energy therethroughwhereby the energy is confined within the drum 56.

In order to further insure that no microwave energy escapes from drum56, the door seat 104 and the inner portion 116 of the door 102 overlapa distance corresponding to approximately firof the wavelength of thefrequency of operation of magnetron 150 whereby the inner portion of thedoor 102 cooperates with the door seat 104 to form a quarter-wave chokejoint to block the passage of microwave energy therebetween.

In operation, wet clothes to be dried are placed in the drum 56 throughthe access opening 100, when the door 102 is in its open position. Afterthe door 102 is closed, the drive motor 74 is energized to beginrotation of the drum 56 and the tumbling of the clothes therein. At thesame time the blower 128 is rotated to create an area of reducedpressure in the drying chamber and thereby create a stream of airthrough the dryer 41 This air stream is drawn into the cabinet 42through the air inlet opening in screen 80, sweeps over the magnetrongenerator 150 and is drawn upwardly through the opening 92 betweenbaffle members 86 and 90, over the heating elements 88 and through theperforations 82 of the drum 56 into the drying chamber thereof. The airstream is then swept over the clothing in the drum 56 and outwardlythrough the perforations 126 in the door 102 into the hollow portionthereof, through the aligned openings 122 and 124 in the door 102 andthe door seat 104, respectively, through the lint screen 143, the frontduct section 132, the wire mesh screen 138 and the rear duct section 134to the blower 128. From the blower the air stream is exhausted throughthe exhaust outlet 140 to the atmosphere.

At this time the magnetron 150 is also energized to produce microwaveenergy at a predetermined high frequency, preferably in this embodimentat 915 MHz. The microwave energy is transmitted along transmission line152 and is radiated by the antenna 158 into the duct front section 132.Duct section 132 propagates the microwave energy toward the lint trap141. It will be noted that transmission of microwave energy through theduct toward the blower 128 is prevented by the wiremesh screen 138 whichserves to reflect the radiated energy thereby to confine it to the ductportion 132. The microwave energy is then transmitted through theaperture provided around the filter screen 143, through the opening 122into the interior of the door 102 and then through the microwave window162 into the drying chamber of the drum 56.

In the drying chamber of the drum 56, the microwave energy isselectively absorbed by the wettest portions of the clothes, serving toheat and vaporize the moisture of water content of the clothing in awell known manner. As the water in the wet clothing is vaporized bymeans of microwave energy, it is carried from the drying chamber of thedrum 56 by the air stream passing therethrough as described above. Inthis manner the wet clothes are quickly and efficiently dried to anydesired degree of dryness. It is an important factor of microwave dryingthat the wettest clothing absorbs the most microwave energy whereby thedrying of heavy materials such as towels which hold a great deal ofmoisture is accelerated considerably while at the same time the lighterclothing which is already dried is prevented from being scorched. Thus,thereis achieved a rapid and uniform drying of each load even though theload may comprise many different weights and textures of materials. I

It will also be noted that the heating and vaporizing of the moisture inthe clothing is accelerated by the fact that the air stream is heatedbefore it passes through the drying chamber of the drum 56 so that iteffects conventionalair convection drying of the wet clothing.

while being able to hold more moisture. This is accomplished by thepassage of the air stream over the heating elements 88 located betweenthe baffle elements 86 and 90. Additional preliminary heating of the airis effected by the passage of the air stream over the magnetron as theair stream enters the cabinet 42 through the intake screen 80. Thus, theair stream serves to cool the magnetron and the heat drawn therefrom isutilized to provide additional warming of the air to enhance its dryingeffect on the wet clothing.

Referring now to FIG. 5 of the drawings, there is illustrated a circuitdiagram for the control means for the dryer 41 and the magnetron 150,the circuit being designated generally by the numeral 170. Circuitincludes the magnetron 150 and a power supply 172 therefor. Circuit 170is coupled through a three wire Edison network which, in a typicalhousehold installation, may provide 236 volts single phase 60 HzAC andincludes ungrounded conductors L1 and L2 and a grounded neutralconductor N. The three conductors terminate in an electricallyinsulating terminal block 174. The power supply 172 is provided with apair of input terminals 176 and 178 coupled respectively to the lineconductors L1 and L2. A first pair of output terminals 180 and 182supply a rectified and filtered DC voltage which constitutes the DCvoltage which constitutes the DC operating potential for the magnetron150. A second pair of output terminals 184 and 186 supply relatively lowvoltage AC power for energizing the magnetron heater.

The output terminal 180 is connected to an input terminal 188 of themagnetron 150 through one coil 190 of a latching relay 192 viaconductors 194 and 196. The latching relay 192 includes a movablecontact 198, a fixed contact 200, a closing coil 202 and the coil 190which functions as an opening coil. The contacts 198 and 200 areconnected in series between the line conductor L1 and the input terminal176 of the power supply 172. The line conductor L1 is also connected toone terminal of the closing coil 202 by means of a conductor 204 and amomentary switch 206. The other terminal of the coil 202 is connected bya conductor 208 to the neutral line N. In addition to the input terminal188, the magnetron 150 is provided with an input terminal 210 which isconnected via a conductor 212 to the output terminal 182 of the powersupply 172. A third input terminal 214 is provided for the magnetron 150and it in turn is connected via conductor 216 to the output terminal 184of power supply 172 while the conductor 218 connects the output terminal186 of power supply 172 to the magnetron input terminal 210.

The anode of the magnetron 150 is represented by a terminal 220 and isconnected to one end of the outer conductor 154 of the transmission line152 as at 222, the inner conductor 156 of the transmission line 152being connected to the input terminal 210. The other end of the innerconductor 156 is connected to the antenna 158 while the other end of theouter conductor 154' .is connected to the duct front section 132 whichin turn is connected to the cabinet 42 as described above and isgrounded as at N for safety purposes. However, since the output ofthemagnetron 150 may not be grounded there is provided a capacitivecoupling 224 in the outer conductor 154 and a capacitive coupling 226 inthe inner conductor 156 to provide DC isolation between the duct section132 and the magnetron 150.

ln'operation, when it is desired to energize the magnetron 150 after thewet clothing has been loaded into the drying chamber of the drum 56 andthe door 102 has been closed, the momentary switch 206 is closed therebyenergizing the closing coil 202 of relay 192. Upon energization of thecoil 202 the movable contact 198 is moved into engagement with the fixedcontact 200 to complete an energizing circuit to the input terminals 176and 178 of the power supply 172. The power supply when energizedprovides the DC and AC operationg potentials for the magnetron 150.

In accordance with the present invention, it has been found that theanode current drawn by the magnetron 150 from the power supply 172 is afunction of the load impedance reflected to the magnetron 150 by the wetclothing in the drum 56. Thus, when a dryer in accordance with theinvention begins to operate, the impedance reflected to the magnetron150 by the relatively high water content of the very wet clothing in thedrum 56 is such that the magnetron anode 220 draws a relatively lowcurrent. However, as the clothes in the drum 56 are dried and themoisture content thereof reduced, the impedance reflected to themagnetron 150 is such that the anode current drawn therebycorrespondingly increases. Accordingly, the current through the openingcoil 190 of the relay 192 also increases. The operating parameters ofthe relay 192 are chosen so that when the clothing has been dried to apredetermined degree of dryness, the anode current of the magnetron 150will be sufficient to energize the C01] 190 to open the contacts 198 and200. In this manner, the power supply cordingly de-energizes when theclothing has been sufficiently dried, thereby de-energizing themagnetron and interrupting the flow of microwave energy therefrom.

It will, of course, be recognized that suitable control apparatus forthe control and cycling of the drive motor 74 and the heating elements88 will also typically be provided in a dryer in accordance with theinvention, such control apparatus being well known in the art. Inaddition, as is well known in the art, interlock switches may beprovided to prevent energization of the magnetron 150 unless the door102 is in its closed position. Further, microwave filters may beprovided in the transmission line 152 to limit propagation therefrom ofharmonics of the frequency of operation of the magnetron 150.

From the foregoing, it will be seen that there has been provided animproved drying machine wherein uniform drying is obtained for materialsof varying weight and absorbency. In addition, there has been providedan electronic or microwave clothes dryer which efficiently utilizes thespace available and existing structure of a conventional home dryer.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein and it is intended to cover inthe appended claims all such modifications which fall within the truespirit and scope of the invention.

What is claimed is:

1. An electronic fabric dryer comprising:

a cabinet having a microwave impermeable drying chamber therein foraccommodating fabrics to be dried;

generating means including a magnetron for producing microwave energy ata predetermined ultrahigh frequency;

air circulating means associated with said drying chamber forcirculating a stream of air therethrough;

a conduit coupling said circulating means with said drying chamberthereby serving as an air duct, said conduit also serving as a waveguideto conduct said microwave energy to said drying chamber;

an air inlet disposed upstream of said magnetron such that said airstream serves to cool said magnetron while said magnetron serves topreheat said air stream;

a heat source disposed in said air stream upstream of said dryingchamber for further heating said preheated air stream before it enterssaid drying chamber thereby serving to accelerate the drying process;

output means coupling said magnetron with said conduit for transmittingenergy from said magnetron to said conduit, whereby moisture from saidfabrics is heated and vaporized by said microwave energy and by saidpreheated air stream and is carried from said drying chamber by said airstream; and

control means associated with said generating means and said heatsource, the control means being responsive to the moisture content ofsaid fabrics to interrupt the transmission of microwave energy into saiddrying chamber and to interrupt the supply of heat to said air streamwhen said fabrics have reached a predetermined degree of dryness.

2. The invention of claim 1 wherein said heat source comprises anelectric resistance heating element.

3. An electronic clothes dryer comprising:

a cabinet having a microwave impermeable drying chamber therein foraccommodating clothes to be dried;

generating means including a magnetron for producing microwave energy ata predetermined ultrahigh frequency; I

a blower associated with said drying chamber for en culating a stream ofair therethrough;

a conduit coupling said blower with said drying chamber, the conduitthereby serving as an air duct;

an air inlet associated with said cabinet and disposed upstream of saidmagnetron such that said airstream serves to cool saidmagnetron whilesaid magnetron serves to preheat said air stream;

a heat source disposed in said air stream upstream of said dryingchamber for further heating said preheated air stream before it enterssaid drying chamber;

output means including a pair of output terminals associated with saidmagnetron and a coaxial transmission line coupled therewith, an antennameans, the free end of the coaxial transmission line being coupled withthe antenna means, the antenna means being insulated from said conduitand positioned to radiate microwave energy into said conduit, saidconduit serving as a waveguide to conduct said radiated microwave energyto said drying chamber in a direction opposite to the flow of airtherethrough; and

control means associated with said generating means and said heatsource, the control means being responsive to the moisture content ofsaid clothes to interrupt the transmission of microwave energy into saiddrying chamber and to interrupt the supply of heat to said air streamwhen said clothes have reached a predetermined degree of dryness.

4. The invention of claim 3 further including a microwave reflectordisposed in said conduit between said blower and said antenna means toprevent the transmission of microwave energy to said blower.

5. The invention of claim 3 wherein:

said cabinet has an access aperture spaced apart from said air inlet theaccess aperture communicating with said drying chamber, and said conduithaving one end thereof terminating adjacent the access aperture;

a hollow microwave impermeable door movable between a closed positionand an open position is provided to control access to said dryingchamber through said access aperture, the door having first and secondopenings therein providing communication with the hollow interiorthereof, the first opening having a microwave window therein foraccomodating transmission of microwave energy therethrough into saiddrying chamber, the first opening also including a plurality ofperforations impermeable to microwave energy but allowing the free flowof air therethrough, the doorin the closed position thereof placing thesecond opening in registry with the free end of said conduit to providea path for the stream of air from the atmosphere to said inlet and saiddrying chamber and said hollow door and said conduit and said blower andfurther to provide a path for microwave energy from said magnetronthrough said conduit and said hollow door and said microwave window intosaid drying chamber.

6. The invention of claim 5 wherein said microwave window comprises agenerally cross-shaped opening in said door, the microwave window havinga cover associated therewith overlying the cross-shaped opening, thecover being transparent to microwave energy while preventing the passageof fabric through the opening into the hollow interior of said door.

7. The invention of claim 6 wherein said drying chamber comprises agenerally cylindrical metallic drum mounted for rotation about asubstantially horizontal axis, the drum having an air ingress and anaccess aperture at spaced-apart points thereof, said air ingress beingimpermeable to microwave energy but allowing the free flow of airtherethrough.

8. The invention of claim 7 further including an electrically conductivedoor seat mounted adjacent said access aperture such that the door seatoverlaps said door in the closed position thereof a distancecorresponding to one-fourth of the wave length of said predeterminedultrahigh frequency thereby providing a choke joint to prevent theescape of microwave energy from said cabinet.

9. The invention of claim 3 wherein said control means comprises a powersupply, a relay having a pair of contacts coupled in series with aninput of the power .supply and a coil winding coupled in series betweenan output of the power supply and an input of said magnetron, the relaybeing responsive to the current through the input of said magnetron foropening the contacts and de-energizing the power supply and saidmagnetron and said heat source when the current through the input ofsaid magnetron reaches a predetermined value as the result of the dryingof the wet fabric to a predetermined degree of dryness.

1. An electronic fabric dryer comprising: a cabinet having a microwaveimpermeable drying chamber therein for accommodating fabrics to bedried; generating means including a magnetron for producing microwaveenergy at a predetermined ultra-high frequency; air circulating meansassociated with said drying chamber for circulating a stream of airtherethrough; a conduit coupling said circulating means with said dryingchamber thereby serving as an air duct, said conduit also serving as awaveguide to conduct said microwave energy to said drying chamber; anair inlet disposed upstream of said magnetron such that said air streamserves to cool said magnetron while said magnetron serves to preheatsaid air stream; a heat source disposed in said air stream upstream ofsaid drying chamber for further heating said preheated air stream beforeit enters said drying chamber thereby serving to accelerate the dryingprocess; output means coupling said magnetron with said conduit fortransmitting energy from said magnetron to said conduit, wherebymoisture from said fabrics is heated and vaporized by said microwaveenergy and by said preheated air stream and is carried from said dryingchamber by said air stream; and control means associated with saidgenerating means and said heat source, the control means beingresponsive to the moisture content of said fabrics to interrupt thetransmission of microwave energy into said drying chamber and tointerrupt the supply of heat to said air stream when said fabrics havereached a predetermined degree of dryness.
 2. The invention of claim 1wherein said heat source comprises an electric resistance heatingelement.
 3. An electronic clothes dryer comprising: a cabinet having amicrowave impermeable drying chamber therein for accommodating clothesto be dried; generating means including a magnetron for producingmicrowave energy at a predetermined ultrahigh frequency; a blowerassociated with said drying chamber for circulating a stream of airtherethrough; a conduit coupling said blower with said drying chamber,the conduit thereby serving as an air duct; an air inlet associated withsaid cabinet and disposed upstream of said magnetron such that saidairstream serves to cool said magnetron while said magnetron serves topreheat said air stream; a heat source disposed in said air streamupstream of said drying chamber for further heating said preheated airstream before it enters said drying chamber; output means including apair of output terminals associated with said magnetron and a coaxialtransmission line coupled therewith, an antenna means, the free end ofthe coaxial transmission line being coupled with the antenna means, theantenna means being insulated from said conduit and positioned toradiate microwave energy into said conduit, said conduit serving as awaveguide to conduct said radiated microwave energy to said dryingchamber in a direction opposite to the flow of air therethrough; andcontrol means associated with said generating means and said heatsource, the control means being responsive to thE moisture content ofsaid clothes to interrupt the transmission of microwave energy into saiddrying chamber and to interrupt the supply of heat to said air streamwhen said clothes have reached a predetermined degree of dryness.
 4. Theinvention of claim 3 further including a microwave reflector disposed insaid conduit between said blower and said antenna means to prevent thetransmission of microwave energy to said blower.
 5. The invention ofclaim 3 wherein: said cabinet has an access aperture spaced apart fromsaid air inlet the access aperture communicating with said dryingchamber, and said conduit having one end thereof terminating adjacentthe access aperture; a hollow microwave impermeable door movable betweena closed position and an open position is provided to control access tosaid drying chamber through said access aperture, the door having firstand second openings therein providing communication with the hollowinterior thereof, the first opening having a microwave window thereinfor accomodating transmission of microwave energy therethrough into saiddrying chamber, the first opening also including a plurality ofperforations impermeable to microwave energy but allowing the free flowof air therethrough, the door in the closed position thereof placing thesecond opening in registry with the free end of said conduit to providea path for the stream of air from the atmosphere to said inlet and saiddrying chamber and said hollow door and said conduit and said blower andfurther to provide a path for microwave energy from said magnetronthrough said conduit and said hollow door and said microwave window intosaid drying chamber.
 6. The invention of claim 5 wherein said microwavewindow comprises a generally cross-shaped opening in said door, themicrowave window having a cover associated therewith overlying thecross-shaped opening, the cover being transparent to microwave energywhile preventing the passage of fabric through the opening into thehollow interior of said door.
 7. The invention of claim 6 wherein saiddrying chamber comprises a generally cylindrical metallic drum mountedfor rotation about a substantially horizontal axis, the drum having anair ingress and an access aperture at spaced-apart points thereof, saidair ingress being impermeable to microwave energy but allowing the freeflow of air therethrough.
 8. The invention of claim 7 further includingan electrically conductive door seat mounted adjacent said accessaperture such that the door seat overlaps said door in the closedposition thereof a distance corresponding to one-fourth of the wavelength of said predetermined ultrahigh frequency thereby providing achoke joint to prevent the escape of microwave energy from said cabinet.9. The invention of claim 3 wherein said control means comprises a powersupply, a relay having a pair of contacts coupled in series with aninput of the power supply and a coil winding coupled in series betweenan output of the power supply and an input of said magnetron, the relaybeing responsive to the current through the input of said magnetron foropening the contacts and de-energizing the power supply and saidmagnetron and said heat source when the current through the input ofsaid magnetron reaches a predetermined value as the result of the dryingof the wet fabric to a predetermined degree of dryness.